1. Field of the Invention
The present invention relates to a paper feed tray unit for a printer which automatically moves slide guides according to a printing paper size input by a user.
2. Description of the Related Art
A paper feed tray unit for a printer of this type is known in the prior art which automatically positions a pair of slide guides at positions spaced from each other by a distance corresponding to a paper size input by a user (refer e.g. to Japanese Laid-open Patent Publication 2000-169020). More specifically, the paper feed tray unit comprises a paper size recognition means for recognizing the size of printing papers placed on a paper support of the paper feed tray unit, and also comprises a motor drive for moving the slide guides closer to or away from each other in opposite directions which are perpendicular to a paper feed direction so as to achieve the automatic positioning of the slide guides.
This printer has end face sensors which respectively move along with the pair of slide guides for detecting width ends of the printing papers, and also has a movement amount sensor which detects the amount of movement of the slide guides, so as to detect the paper size. When printing papers are placed on the paper support of the paper feed tray unit, the size of the printing papers is detected by the end face sensors and the movement amount sensor so as to actuate the motor drive to move and position the slide guides according to the thus detected paper size.
Another paper feed tray unit for a printer for the positioning of a pair of slide guides is known in the prior art, in which when printing papers are placed on a paper support of the paper feed tray unit, the slide guides are moved to positions spaced from each other by a minimum distance, while the thus placed printing papers are aligned with each other at a predetermined location. This paper feed tray unit has position sensors placed thereon at positions which are spaced from each other in a direction perpendicular to a paper feed direction, and which respectively correspond to standard sizes of printing papers so that the position sensors detect the paper size of the printing papers placed on the paper feed tray unit. The printer has a motor drive which is actuated to move and position the slide guides according to the thus detected paper size (refer e.g. to Japanese Laid-open Patent Publication 2003-128271).
However, such prior art paper feed tray units require the slide guides to be on standby at positions spaced from each other by a maximum distance before the printing papers are placed on the paper support, because the width of the paper size of the printing papers is detected after the printing papers are placed on the paper support. Thus, there is a possibility that a user cannot set printing papers at a predetermined location when placing them on a paper support, so that when the slide guides move to move the printing papers to a predetermined position, or to detect the width of the paper size of the printing papers, the slide guides may crush the printing paper, causing problems such as paper jam at a paper inlet or inside the printer.